U.S. Pat. Nos. 5,008,718 and 5,233,204 disclose conventional LEDs having a transparent window layer. With these structures the well-known crowding effect is improved and the light from the surface of the LEDs is increased. Therefor, the brightness of the conventional LEDs is significantly increased. However, The conventional LEDs do not give the highest desired light brightness because the brightness is affected by many factors, such as crowding effect, incident light critical angle, substrate light absorption, etc.
U.S. Pat. Nos. 5,237,581 and 4,570,172 disclose DBR LEDs having a semiconductor multilayer reflector i.e., Distributed Bragg Reflector. The DBR of LEDs reflect the light incident into the substrate back to emit from the DBR LED. The light brightness of the DBR LEDs is increased. However, the addition of multilayer reflector forms many hetero junctions and thus the driving voltage or the power consumption of the DBR LEDs is increased.